Vinyl fluoride polymerization and aqueous dispersion of vinyl fluoride polymer

Abstract

A process for producing vinyl fluoride polymer comprising polymerizing vinyl fluoride in an aqueous polymerization medium containing initiator and halogen-free surfactant with a critical micelle concentration of less than about 0.05 weight percent at 25° C. The halogen-free surfactant is present in the aqueous polymerization medium in an amount less than about 0.1 weight percent based on the weight of the aqueous polymerization medium. The aqueous polymerization medium is essentially free of halogen-containing surfactant. An aqueous dispersion comprising vinyl fluoride polymer particles present in a range of from about 5 to about 40 weight percent based on the weight of the aqueous phase, wherein said vinyl fluoride polymer particles have a Dv(50) of less than about 20 microns, and halogen-free surfactant, wherein said halogen-free surfactant is present in said aqueous dispersion in an amount less than 0.1 weight percent based on the weight of the aqueous phase.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the polymerization of vinyl fluoride in an aqueous polymerization medium and an aqueous dispersion of vinyl fluoride polymer.BACKGROUND OF THE INVENTION[0002]Poly(vinyl fluoride) (PVF) is used in film form for a variety of protective and decorative applications. Because of its proven weatherability and moisture barrier properties, poly(vinyl fluoride) is particularly desirable for use as a protective layer in backsheets for photovoltaic modules.[0003]The polymerization of vinyl fluoride (VF) to produce PVF has typically been carried out in water as the polymerization medium and by employing a water soluble organic azo-type initiator such as 2,2′-azobis(2-amidinopropane)dihydrochloride and 2,2′-azobis(N,N′-dimethyleneisobutyroamidine)dihydrochloride to yield a highly fluid aqueous dispersion or slurry of very finely divided polymer particles. Polymerizations of this type, in which the initiator is water soluble and the mono...

AI Technical Summary

Benefits of technology

The process enables the production of PVF with higher solids content and improved particle size control, reducing coagulum formation and large particle aggregates, thus enhancing film quality and reactor efficiency.

Problems solved by technology

In processes of this type, significant limitations and problems have been encountered.

If it is attempted to increase the solids content, coagulum (undispersed polymer which must be discarded as waste) results and / or undesirable particle aggregates form which can cause defects in film made from the dispersion.

In continuous processes which produce a slurry of aggregates of primary PVF particles, a significant problem encountered is the broad particle size distribution of the polymer particles formed.

Larger particles, such as those above 30 μm, produce defects in polyvinyl fluoride film formed from the PVF polymer resin and cause reactor scaling, requiring periodic shutdowns for reactor cleaning.

This necessarily limits the capacity of the reactor and has been found to be only partially successful in preventing the formation of large particles.

However, because of environmental concerns which have been raised concerning APFO and because fluorosurfactants are expensive, a polymerization process employing a halogen-free surfactant would be desirable.

While these surfactants are compatible with the organic azo-type initiators, when used in the polymerization of vinyl fluoride in the amounts typically used in hydrocarbon polymer polymerizations, they produce low yields of low molecular weight PVF products that are not useful in typical applications for PVF.

While these surfactants are also compatible with organic azo-type initiators, U.S. Pat. No. 5,229,480 to Uschold shows that the use of surfactants of this type produce PVF of low molecular weight in reduced yields and often contribute a highly undesirable yellow color to the polymer.

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